Cast Mo–Cr, W–Cr, and Cr–Al master alloys were prepared via centrifugal SHS metallurgy. The effect of variation in component fractions in green mixtures (100 – α)(Cr2O3 + Al) + α(MoO3 + Al) and (100 – α)(Cr2O3 + Al) + α(WO3 + Al) on the synthesis of Mo–Cr and W–Cr alloys, respectively, was thermodynamically analyzed. Thermodynamic calculation of Cr–Al master alloy production was presented and provided the necessity of using a complex oxidizing agent, chromium(III) oxide and chromium(VI) oxide in a certain ratio. Experiments for Mo–Cr, W–Cr, and Cr–Al systems proved the necessity of applying overloading at an acceleration of no less than 50 g to prolong the lifetime of the melt. Introduction of functional additives CaF2 (fluorspar) and sodium hexafluoroaluminate Na3[AlF6] (cryolite) to the green mixture lowered the melting temperature of the slag phase (reduced its viscosity) and facilitated the phase separation. EDS and mass spectroscopy analyses showed that the chemical compositions of synthesized master alloys are close to their calculated and target values. XRD results revealed the existence of solid solutions based on target elements.

Cast Mo–Nb–Ta–(Cr,V,Zr,Hf) refractory high-entropy alloys were first prepared via gravity-assisted SHS metallurgy. It was shown that the ingots crystallize from the liquid state, in which a homogeneous distribution of constituting elements is provided. The phase composition of synthesized RHEA ingots was revealed to be doped component dependent. Combined reduction of metals of V (Nb, Ta, V) and VI (Cr, Mo) groups formed single-phase alloys with a bcc crystal structure. MoNbTaCr alloys doped with Zr or Hf having hexagonal crystal structure were found to consist of fcc and hcp phases in addition to bcc solid solution.

A thermoelectric Co2TiAl alloy was obtained by the SHS-metallurgy method for the first time. The microstructure and the magnetic and thermoelectric properties of the synthesized alloy were investigated. The maximum value of the Seebeck coefficient and thermoelectric power at room temperature were ‒29.5 μW/K and 1230 μW m–1 K–2, respectively. The comparison of the influence of the SHS-method modifications on the properties of the synthesized alloy was made. It has been shown that the alloy synthesized by SHS pressing has higher thermoelectric characteristics than the alloy obtained by the SHS-metallurgy method.

High-entropy alloys were produced by centrifugal self-propagating high-temperature synthesis and used as precursors for preparation of catalysts for CO and propane deep oxidation and CO2 hydrogenation. The precursors were converted into catalysts by aluminum leaching and stabilization with hydrogen peroxide solution. Prepared FeCoNiCu, FeCoNiCuMo, FeCoNiCuMn, and FeCoNiCuCr catalysts were characterized by XRD, SEM/EDS, and BET methods and tested in the processes of deep oxidation of CO and propane and methanation of CO2. The highest CO2 conversion, 50.6

Keywords: composite materials, master alloy, chromium, centrifugal SHS

Previously, we suggested a new class of polymetallic catalysts based on SHS-produced intermetallic compounds for environment-friendly deep oxidation of CO and hydrocarbons [1]. Among these, Co–La catalyst showed best catalytic activity in the Fischer– Tropsch synthesis [2]. Since Co is also active in oxidation reactions [3], we made an attempt to further improve the oxidative ability of SHS-produced Co–La catalyst upon its modification with copper [4]. Moreover, Co and Cu catalysts exhibited high activity in the hydrogenation of СО2 [5–7]. Cu-doped Co–La catalysts of nominal composition (95 – x)Co–xCu–5La (x = 10, 30, 50 wt %) were prepared by centrifugal SHS from Co3O4–Cu2O–Al– La powder mixtures. As-prepared intermetallics were leached with NaOH, stabilized by processing in H2O2 solution (for details see [1, 2]), and characterized by SEM/EDS (Zeiss Ultra plus microscope + JCXA-733 Superprobe JEOL accessory) and XRD (DRON-3, Fe-Kα radiation). The 100–300 μm fractions of SHSproduced catalyst were tested for their activity in a flow silica reactor as described in [1, 2]. Gas compositions were determined using an Avtotest 02.03P gas analyzer and a gas-liquid chromatograph Model 3700.

Polymetallic Co90–V10 catalyst was derived from an SHS-produced Co–V–Al precursor and its performance in the deep oxidation of СО, propane and in the СО 2 hydrogenation was determined and compared with that of previously synthesized Co100 and Co95–V5 polymetallic catalysts. The precursor and catalyst were characterized by XRD, SEM, and BET analyses. In the processes of deep oxidation, Co90–V10 catalyst showed the best results. The CO 2 hydrogenation turned independent of V content of catalyst. A maximum of CO 2 conversion (65% at 350°C) was exhibited by Со100 catalyst. The СО 2 conversion over Co100 and Co95–V5 catalysts was found to show a maximum at a gas hour space velocity (GHSV) of 6000 h –1 .

Проведен обзор результатов, полученных авторами по синтезу литых жаропрочных сплавов методами СВС-металлургии. Основное внимание уделено синтезу жаропрочных сплавов на основе интерметаллидов никеля и титана, кобальта и силицидов ниобия. Определены параметры, позволяющие управлять процессами горения исходных смесей термитного типа, гравитационной сепарацией в расплаве продуктов горения, формированием состава и структуры литых жаропрочных сплавов.

A promising approach to the development of advanced metallic materials is based on a fundamentally new concept of avoiding the use of the main component but mixing several metal elements simultaneously. Such multicomponent alloys are called high-entropy alloys, the most studied of which is the Co-Cr-Fe-Ni-Mn alloy with attractive mechanical properties. The single-phase fcc structure is stable in this alloy, which allows it to be used as a "model" high-entropy alloy or a single-phase multicomponent solid solution. This paper is the first to experimentally evaluate the possibility of synthesizing strengthened high-entropy alloys with the basic system (Co-Cr-Fe-Ni-Mn) and strengthening precipitates based on borides and silicides of refractory metals (Mo and Nb), formed in situ during the combustion of thermite-type SHS systems. The microstructural analysis of the synthesized NiCrCoFeMn alloys with the complex modifying Mo(Nb)-Si-B additive showed that, at a higher content of the additive, the microstructure of the synthesis products exhibits the high-entropy alloy matrix and precipitates of new structural elements based on borides and silicides of refractory metals (Mo and Nb). The morphology and concentration of such precipitates depends on the concentration of the additive in the green mixture. The strengthening precipitates are of endogenous origin as they are formed in situ during SHS and are the result of chemical reactions occurring both directly in the combustion wave and during cooling of the high-temperature melt of the synthesis products. Control of SHS processes opens up new possibilities for the formation of metal-matrix composites based on high-entropy alloys.

The influence of different methods of producing alloys of the Fe–Cu system from immiscible components is studied. Alloys with limited solubility (LS) in liquid and solid states are impossible to fabricate by conventional metallurgy. This is why developing low-cost and simple technologies for fabricating such alloys and materials based in them, making it possible to specify the necessary level of physicomechanical properties, is currently a relevant problem. Energy-effective SHS metallurgy is used for the first timchemical scheme of the synthesis ofe in this work to prepare a pseudoalloy with a composition, wt %, of 70Cu–30Fe from oxide materials. This technology offers the use of chemical energy liberated during the interaction of highly exothermic thermite compositions (in a combustion mode), which makes this method one of most energy-efficient for cast material production. The short synthesis time (tens of seconds) and protection of the top ingot surface by the oxide melt (Al2O3) against oxidation make it possible to perform the process in atmospheric conditions. Rods with the same composition have been fabricated by vacuum induction smelting from pure (impurity-free) components Fe and Cu for a comparative analysis of structural components of alloy samples. It is revealed that the high temperatures of the melt of the SHS alloy provide an increased solubility of Cu in Fe. Then structural components are isolated during the crystallization in the form of finely dispersed particles over the entire volume, forming the hierarchical structure characteristic for the SHS alloy only. The 70Cu–30Fe alloys formed in the combustion mode (SHS) have a uniform homogeneous structure with a uniform distribution of all structural components over the sample volume, which can be of great practical interest, in particular, when developing isotropic and anisotropic hard-magnetic materials with high magnetic energy.

A relatively new approach to obtaining metal materials containing several principal elements in equiatomic concentrations which look promising for replacing commercially used alloys is proposed. Such materials are called high-entropy alloys (HEAs). Studies show that HEAs tend to form a simple solid-solution structure and can also contain ordered intermetallic phases. Such a method of forming metal materials can be regarded as a background for producing new HEAs with elevated performance characteristics. Most studies focus on the relationship between microstructure and measured properties; significantly less attention is paid to studying and developing new effective methods for creating HEAs. In this paper, we study the possibility of obtaining CoCrFeNiMn–(X) HEAs by centrifugal metallothermic SHS. Chemical and technological modes of modifying cast CoCrFeNiMn alloy during synthesis (in situ) by introducing alloying components into the starting exothermic compositions are tested for the first time. The microstructure and phase composition of NiCrCoFeMn alloys synthesized from mixtures containing Ti–Si–B(C) or Al are characterized. The microstructure of CoCrFeNiMn–(Ti–Si–B(C)) HEAs is found to consist of an HEA-based matrix and new structural inclusions of carbides and borides of titanium. High-Al CoCrFeNiMn–Al HEAs are represented by a composite structure containing NiAl as a basis and dispersion nanoprecipitates (~100 nm) of a Cr- and Fe-based solid solution.

A comprehensive comparative study of the structure, phase composition, and mechanical properties of heat-resistant nickel-based Ni–Cr–(X) alloys produced by the methods of traditional metallurgy and self-propagating high-temperature synthesis (SHS metallurgy) is carried out. With the purpose of formation of the submicrocrystalline structure, a longitudinal rolling and post-deformation annealing of the cast alloy is performed. The microstructure of the heat-resistant alloys is investigated by the SEM and TEM methods. It is shown that the cast alloy has a recrystallized structure with the mean grain size of ~1 μm and the particles of chromium carbides have a size of ~1–3 μm. After rolling and subsequent annealing (750°C/1 h), the average grain size is reduced to 0.43 μm and the formation of dispersed particles of carbides 100 nm in size is observed. The structure of the alloy obtained by SHS metallurgy is dendritic, and particles of W and Cr are absent. When 0.1 wt % carbon powder is added to the initial powder mixture for SHS synthesis, formation of the network of W and Cr particles is observed along the boundaries of dendrite colonies. It is found that the SHS Ni-based heat-resistant alloy similar in composition to commercial cast alloy is characterized by improved mechanical properties and increased heat resistance compared to the cast alloy in both the coarse-grained and the submicrocrystalline state. Adding the carbon powder to the powder mixture for SHS leads to a further increase in the resistance to high-temperature deformation owing to formation of the carbide phase impeding the movement of dislocations and grain boundary creeping processes.

The possibility of utilizing the industrial wastes of metallurgical production and secondary raw materials (aluminum) by organizing self-propagating high-temperature synthesis (SHS) and obtaining cast ferroalloys (Fe–Si; Fe–Si–Al, and Fe–Si–Al(Cr, Mn)) was investigated. The main production operations of the preliminary preparation of the starting raw materials were worked out and cast ferroalloys providing high concentration Si, Al and B were revealed. The possibility of processing the industrial wastes of metallurgical production and obtaining cast ferroalloys was shown.

TiAl-based composite materials have been produced by spin-casting self-propagating high-temperature synthesis metallurgy methods using thermite-type mixtures, general relationships in the formation of their composition and structure have been investigated, the synthesis conditions have been optimized, a method for obtaining large ingots has been proposed, and their composition and structure have been determined. We have obtained cast Nb- and Cr-doped TiAl-based composite materials using mixtures of Ti, Nb, Cr, and Ca oxides with a combined reducing agent (Al and Ca) under the effect of an overload above 200g. It has been shown that partial Ca substitution for Al in the starting mixture ensures complete reduction of the TiO2, and the resultant metallic phase contains calculated amounts of Ti and Al. Mixtures of optimized composition make it possible to produce a cast composite material similar in composition to alloy 4822.

The laws and mechanism of combustion of TiO2 based thermite systems with a complex reducing agent (Al and Ca) under the influence of overload are revealed. The thermite system includes a basic composition whose combustion products are target elements (Ti, Al, Nb, and Cr) and a high-energy additive (CaO2, Al, and Ca) for ensuring high-temperature combustion. With the introduction of an energy additive, the system acquires the ability to burn. With a sufficient content of this additive, the combustion products (TixAly and Al2O3 and CaO oxide solutions) can melt. As the fraction of Ca in the base mixture composition increases, the burning rate drops and the reduction completeness of the target oxides increases. With an optimal ratio of Ca and Al in the mixture, the yield of the target elements in the ingot is close to the calculated value.